I have had multiple retinal detachments and have large clouds of floaters, which make it challenging to complete CAPTCHAs. When I try a few and fail I ask for help from people nearby when someone is available. Often I have to do several before finding one I can pass. I think the only good news is that I have yet to have one say I have used up all my chances. I agree they do not make these for people with vision limitations, although occasionally I am given the option of listening to the CAPTCHA.